Rolling mill apparatus for high pressure generation

ABSTRACT

A rolling mill/matrix combination capable of bringing about high pressure, high temperature conversions in a substantially continuous sequence is described. The material being subjected to high pressure is disposed within a series of separate sample containment pockets in a sheet of matrix material and the composite is compressed between a rolling metal element and a flat metal plate forcefully urged toward each other. Means are also set forth for direct heating of the sample material, while high pressure is applied thereto. The synthesis of cubic diamond is exemplary of the high pressures, high temperatures simultaneously attained with this apparatus.

United States Patent Robert S. Kirk Seotia, N.Y.

May 21, 1969 Mar. 23, 1971 General Electric Company 1 ROLLING MILL APPARATUS FOR HIGH PRESSURE GENERATION Inventor Appl. No. Filed Patented Assignee 6Cldnts,5DrawingFigs.

736,217 8/1903 Clark References Cited UNITED STATES PATENTS 3,103,038 9/1963 Zolton ABSTRACT: A rolling mill/matrix combination capable of bringing about high pressure, high temperature conversions in a substantially continuous sequence is described. The material being subjected to high pressure is disposed within a series of separate sample containment pockets in a sheet of matrix material and the composite is compressed between a rolling metal element and a flat metal plate forcefully urged toward each other. Means are alm set forth for direct heating of the sample material, while high pressure is applied thereto. The synthesis of cubic diamond is exemplary of the high pressures, high temperatures simultaneously attained with this apparatus.

PATENTED HAR23 l9?! SHEET 2 0F 2 FIG. 5

IN l E N TOR: R0 ERT s. K/R

HIS "ATTORNEY lEhllLLllNG MILL APPARATUS Emil llllll Gllil PRESSURE GENERATTGN BACKGROUND OF THE TNVENTION Static high pressures having a magnitude in excess of about l ltilobars (l lrilobar equals 987 atmospheres) have been attainable for many years. However, all of the apparatuses having this capability have the limitation of batch-operation in which complex arrangements are employed to contain the sample being subjected to high pressure (and usually simultaneously being subjected to high temperature). In such apparatuses once the high pressure application to a given sample has been accomplished in order to repeat the given sample has been high pressure process, the pressure must be released, the sample containment chamber opened up and the sample removed for replacement by a new sample. One particularly successful high temperature, high pressure apparatus is that described in US. Pat. No. 2,94l,248l-Iall, which has been commercially employed for a number of years to produce synthetic diamonds by the methods described and claimed in US. Pat. No. 2,947,609-Strong and US. Pat. No. 2,947,610- -i lall et al. The aforementioned US. Patents are incorporated by reference for descriptions therein of useful high strength materials for preparing structures for the application of high pressure and conditions for diamond synthesis.

The economics of high pressure synthesis should be considerably improved by simplification of the sample arrangement and reduction of the batch cycle time, preferably to the point of enabling substantially continuous sequential high pressure (or high pressure/ high temperature) conversions.

SUMMARY OF THE INVENTION The rolling mill apparatus of this invention comprises the combination of a rolling element coacting with a sheet of matrix material disposed between a pair of flat plates substantially parallel to each other. Means are provided to laterally displace the plates relative to each other and also to simultaneously forcefully urge the plates toward each other thereby causing the rolling element to compress the matrix. The sample material being exposed to high pressure is disposed within a series of spaced conversion pockets in the sheet of matrix material. As portions of the sheet of matrix material are compressed, the conversion pockets containing sample material therein are compressed as well. Successive portions of the matrix sheet are compressed as the two plates are laterally displaced relative to each other. Means for the direct electrical heating of electrically conductive samples is provided.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a cross-sectional view through the rolling apparatus of this invention showing the several elements thereof; and matrix lFlG. 2 is a schematic representation showing the relationship between the coacting rolling element and matrix sheet under static pressure conditions and, as well, a graphic representation of the pressure distribution correlated therewith;

EEG. 3 is similar to FIG. 2, but shows the relationship between the coacting rolling element and matrix sheet and the change in pressure distribution upon advancement of the rolling element;

EEG. l is a three-dimensional view of a sheet of matrix material and one arrangement for a plurality of sample placements. Part of the sheet has been subjected to compression, the relationship of the rolling member to the compressed portion being shown in dotted lines; and

H6. 5 is a sectional view through an exemplary sample as would be taken on line 5-5 of FllG. 4.

DEECRlPTIOIN OF THE PREFERRED EMBODIMENT The combined rolling/matrix apparatus llll shown in FIG. it approaches a continuous flow process high pressure system in that by means of matrix sheet ll samples may be introduced and removed from a high pressure region in a substantially continuous sequence.

As is seen in FIG. l, a downward force is exerted by a press (not shown) on upper flat plate l2 forcing roller element l3 toward lower flat plate M, while at the same time a laterally directed force applied to plate M resting on rollers l5 causes lateral displacement between plates 12 and id. This displacement in turn causes both rotation and translation of roller H3.

The instant invention is designed and operated in direct contrast to metal rolling apparatus and operations in which great pains are taken. to limit the maximum hydrostatic stresses generated in the workpiece. Thus, in metal rolling lubrication, heating and stretching are employed in combination in order to restrict maximum rolling pressures to the 10 to 20 kilobar range. On the contrary, by eliminating the lubrication, stretching and heating (except for heating at the sample sites, if desired) considerably higher pressures than were previously realized can be generated By way of illustration, if a high strength metal shape were to be coated with an abrasive material and cold rolled without applying tension thereto during the rolling operation, very high pressures can be generated.

Now it has been found that by employing a highly compressible matrix sheet ll formed of a material: (a) which exhibits shear strength that increases greatly under the application of increasingly high pressures, (b) which exhibits a high coefficient of friction so as to coact with the smooth surface of roll 13 with a gripping action and (c) which maintains a cohesiveness or continuity (i.e. does not fracture as roller 13 proceedstherealong) such that the matrix sheet lll will be continuously drawn through the high pressure throat region to, very high pressures may be applied to the sheet It and to samples embedded in and laterally confined thereby.

The best available matrix materials appear to be those, which contain distributed therethrough fine, hard gritty material, such as quartz or iron oxide. To quantitatively designate the shear strength requisite of such materials a gross coefiicient of internal friction may be employed. This coefficient of internal friction may be defined as the ratio of the shear strength of the given material to the compressive stress applied thereto. Suitable rolling matrix materials will exhibit coefficients of internal friction as high as possible, preferably above 0.4.

Additional considerations for the combined system are illustrated in FIGS. 2 and 3. FIG. 2 illustrates the conditions of pressure prevailing, when the element T3 is subjected to static pressure conditions (downward force only), while FIG. 3 illustrates the prevailing conditions of pressure and the reshaping of the matrix as soon as an additional horizontal force is imposed to start movement of rolling element l3 to the left (in the drawing). Under static pressure conditions, the applied load is distributed over the arcuate surface l7, ill, l9 symmetrically about point 18 with the maximum pressure being exerted at point 118.

As won as the rolling element 13 beings to move to the left, the interface area available between roll 13 and the matrix material ll, a) for supporting the applied load and b) for developing the friction force necessary for roller lid to grip the matrix material ll and impose lateral stresses upon it sufficient to force it through the extrusion sequence (wherein it is compressed and passed through throat region 116) is reduced by approximately one-half (compare arc l7, l8, T9 with are 2t, 22, 23:). Providing that the elastic limit of rolling element l3 is not exceeded and with a matrix material having a gross coefficient of internal friction approaching unity, the pressure at point 23 (rolling posture) would be greater than twice the pressure existing at 18 (initial static condition), because the area under the initial static pressure distribution curve 24 and rolling posture pressure distribution curve 26 must remain the same. As may be seen comparing curves 7% and 2b, the pressure reached at point 23 fails far short of being greater than twice the pressure at point iii. The reason for this is that matrix materials known to date, e.g. pyrophyllite, catlinite, talc, boronafrlled epoxy, etc. each has a gross coefficient of internal friction in excess of 0.4 but do not approach the ideal 1.0 value for this coefficient. However, other important characteristics are exhibited as well. For example, the requisite coefficient of friction between pyrophyllite and tungsten carbide is ample to effect the extrusion through throat 16, while at the same time the matrix sheet 11 of pyrophyllite, although brittle, does not fracture immediately ahead of roller 13. If such fracture did happen it would not be possible for the relative movement between matrix sheet 11 and roller 13 to occur whereby entry of the matrix sheet 11 between roller 13 and plate 14 is accomplished.

Another very important capability, which must be exhibited by the matrix material 11 during pressure generation by rolling, is that the tolling element 13 must be supported thereby not only while the pressure is increasing (matrix material entering high pressure region 16), but also while the pressure is decreasing (matrix material leaving region 16 is compressed, deformed state) in spite of the extrusion of the matrix material during this time.

Another aspect of concern in the development of rolling pressures in the practice of this invention is the magnitude of the pressure generated between upper flat plate 12 and roll 13. Reduction of this pressure may be accomplished (a) by proportioning the width of contact between upper flat 12 and roll 13 to the width of contact between roll 13 and matrix material 11 so that the former is at least several times greater than the latter and (b) by introducing a thin sheet of metal 27, as for example stainless steel, between upper fiat l2 and roll 13 to distribute the load more evenly over the contact surface. This sheet 27 should be hard enough to support the load, but ductile enough to spread and achieve the maximum contact area available between plate 12 and roll 13 and better transmit the load. Thus, in the structure shown in FIG. 1 as rolling proceeds sheet 27 would be rolled over the top of roller 13 at the same time as matrix sheet 11 is rolled along the bottom of roller 13.

The sheet of matrix material 11 as shown in FIG. 4 illustrates an exemplary arrangement of cylindrical samples sites 28 each of which would contain a cylindrical sample 29. The right-hand portion of sheet 11 (as shown in FIG. 4) represents compressed and extruded matrix material containing compressed, deformed samples 29 which have been subjected to the high pressures generated by roll 13 illustrated in dashed lines.

The rows of sample sites 28 extending parallel to roller 13 should be separated by a distance controlled primarily by roller diameter. Thus, sufficient matrix material should remain between sites 28 so that the pressure gradients created during operation will be supported. If sample sites were to be superimposed upon FIG. 3, and one row were to be located centered at point 23. The leading edge of the next row of sample sites should preferably not extend closer thereto than point 21. Spacing in the roller direction is not critical and conceivably bar-shaped samples disposed in the direction of the roller axis may be used.

Originally, in selecting gasket materials, which could be useful for containing solid samples 29 pyrophyllite (a stone presently used in the belt type high temperature apparatus described in the aforementioned Hall patent as a gasket and insulating material) was initially rejected as unsuitable for the instant application, because of its brittle nature. It was believed that in having to coact with a compressing, rolling element a sheet of pyrophyllite would not be able to draw itself" into high pressure region 16, because of the likelihood of fracture of the sheet before compression and extrusion could occur. However, in spite of the fact that at atmospheric pressure pyrophyllite is a brittle material, when this material is subjected to high pressures it exhibits a surprising willingness to draw itself into the high pressure throat region 16.

The effectiveness of pressure buildup within the pyrophyllite sheet matrix during the application of rolling compression/extrusion was determined experimentally by observing the resistance changes accompanying the 24 and 88 kilobar transformations in bismuth. Bismuth wire surrounded by a sodium chloride sheath for lateral support was inserted into a 0.014 inch hole 28 drilled through a matrix sheet 11 of pyrophyllite. The wire extended through to both sides of the pyrophyllite sheet so as to make contact with both the roll 13 and flat 14. The 88 kilobar transition in the bismuth was achieved while rolling a Z /iainch diameter tungsten carbide roll at a speed of 36 mils per minute under a vertical load of 15 tons. Also, it was found that when the rolling mill was stopped the prevailing high pressures were maintained.

The synthesis of diamonds using the roller/matrix combination of this invention as accomplished in a nickel (32)/antalum (33) composite sample embedded in pyrophyllite. The sample extended through [graphite sheet 11 and passed through the high pressure region with only a small amount of distortion. When contact was actually made graphite 31 to both the roll 13 and flat 14, the sample was heated by passing about 50 amperes of current therethrough. Electric current was supplied from a power source (not shown) via electrical connector 33, plate 12, sheet 27, roll 13, sample 31, plate 14 and electrical conductor 34 back to the power source. This resistance heating was sufficient to melt nickel disc 32 (a temperature in excess of l,400 C. of approximately 60 kilobars the melted nickel catalyzed the formation of diamond from graphite 31. Tantalum disc 33 serves as a scavenger to clean up the reaction environment from gaseous product of pyrophyllite decomposition.

The apparatus of this invention may be employed for the simultaneous application of high pressures and high temperatures either by stopping the roll 13 once the highest pressures are being generated in the sample 29 and then closing the heating circuit to pass the heating current through the sample or with the proper coordination of controls (not shown) heating may be automatically synchronized with the position of rolling element 13.

The cubic diamond material formed was polycrystalline (compacts) with individual faces approximately 50 across. Positive identification was made from X-ray patterns, and comparison with cubic diamond material grown in static systems.

It has also been found that liquid samples may be compressed (statically) in porous membranes in which the pores are not connected. A particular example has been an etched polycarbonate film with transversely extending pores about 8 microns in diameter. The porous, impregnated film maintained its integrity and contained the liquids through pressure applications in excess of about 15 kilobars indicating that in a dynamic situation new samples could be drawn into the high pressure region 16.

it is necessary that the liquid wet the porous film matrix in order to fill the sample holes. If necessary, the liquid may be made to wet the film by the addition of a detergent. In order to conduct high pressure/high temperature reactions it may be necessary to substitute porous mica for the polycarbonate film, the sample being indirectly heated locally by means of an annular liner of carbon film within each sample-receiving pore.

Although the apparatus arrangement shown in FIG. 1 is preferred. A second roller can be substituted for lower plate 14 as a variation thereof. Also, if desired the sheet of matrix material 11 may be flanked (top and bottom) with thin flexible sheets of electrically conducting metal. In such a modification the heating currentcan be introduced into the samples using the metal sheets themselves.

The thicknesses of sheets of pyrophyllite matrix material actually employed with a ZVzdiameter tungsten carbide roll have been about 50 mils thick. However, sheet thicknesses to be used in the practice of this invention will scale up as an approximate function of roll diameter, e.g. with a SVz-inch diameter roll the sheet thickness (using pyrophyllite) could be about mils. Using other matrix materials, those having larger coefficients of internal friction than pyrophyllite may be somewhat thicker for a given size roll, while those matrix materials having smaller coefficients of internal friction than pyrophyllite will have to be thinner than the pyrophyllite sheet ordinarily selected for a given roll diameter. 5

lclaim:

1. A high pressure apparatus comprising in combination:

a. cooperative first and second relatively rotatable elements adjustable to predetermined spaced juxtaposition to define a throat region therebetween, at least one of said elements being a smooth rotatable roller;

b. means connected to at least one of said elements for causing relative rotation therebetween;

c. means in force-transmitting relation to at least one of said elements for forcing said elements towards each other. during relative rotation thereof; and

d. a sheet of matrix material disposed for continuous insertion into and compression in said throat region, said sheet having a plurality of spaced sample sites located therein and extending substantially perpendicular to the major surfaces of said sheet, the initial thickness of said sheet and original heights of said sample sites being significantly greater than the spacing between said elements;

ll. said matrix material (a) coacting with the smooth surface of said roller so as to be gripped thereby. (b) having sufficient cohesiveness to support continuous insertion, and (c) having a coefficient of internal friction of at least about 0.4.

2. The high pressure apparatus as recited in claim ll wherein the first and second elements are a roller and a flat plate supported on rollers, respectively.

3. The high pressure apparatus as recited in claim 1 wherein the matrix material is pyrophyllite.

4. The high pressure apparatus as recited in claim 1 having additional means connected thereto for heating the samples during compression thereof.

5. The high pressure apparatus as recited in claim 1 having as part of the forcing means a flat plate in force-transmitting relationship with the roller and having a thin flexible sheet interposed between said plate and said roller.

6. The high pressure apparatus as recited in claim 1 wherein the sample sites are arranged in a pattern to enable simultaneous application of high pressures to a plurality of samples. 

1. A high pressure apparatus comprising in combination: a. cooperative first and second relatively rotatable elements adjustable to predetermined spaced juxtaposition to define a throat region therebetween, at least one of said elements being a smooth rotatable roller; b. means connected to at least one of said elements for causing relative rotation therebetween; c. means in force-transmitting relation to at least one of said elements for forcing said elements towards each other during relative rotation thereof; and d. a sheet of matrix material disposed for continuous insertion into and compression in said throat region, said sheet having a plurality of spaced sample sites located therein and extending substantially perpendicular to the major surfaces of said sheet, the initial thickness of said sheet and original heights of said sample sites being significantly greater than the spacing between said elements;
 1. said matrix material (a) coacting with the smooth surface of said roller so as to be gripped thereby, (b) having sufficient cohesiveness to support continuous insertion, and (c) having a coefficient of internal friction of at least about 0.4.
 2. The high pressure apparatus as recited in claim 1 wherein the first and second elements are a roller and a flat plate supported on rollers, respectively.
 3. The high pressure apparatus as recited in claim 1 wherein the matrix material is pyrophyllite.
 4. The high pressure apparatus as recited in claim 1 having additional means connected thereto for heating the samples during compression thereof.
 5. The high pressure apparatus as recited in claim 1 having as part of the forcing means a flat plate in force-transmitting relationship with the roller and having a thin flexible sheet interposed between said plate and said roller.
 6. The high pressure apparatus as recited in claim 1 wherein the sample sites are arranged in a pattern to enable simultaneous application of high pressures to a plurality of samples. 